In the case of a workpiece machined in a machine tool, one definitive requirement of its surface is that it must be manufactured inexpensively from the standpoint of the function to be fulfilled by the surface of the workpiece (e.g., bearing surface, conductivity, visible surface, adhesive strength, friction, seal). To do so, the properties of the surface (e.g., low friction, large contact area, defined minimum roughness, sharp tips, low abrasion) must be defined as precisely as possible and verified within the context of production, so that the intended function can be optimally satisfied by the surface.
Real workpiece surfaces (actual surfaces) deviate from their ideal shape (ideal surface). These differences are subdivided into several categories. The actual surface is divided into waves of different wavelengths. The wavelength decreases with the order of the deviations in shape (first order: deviation in shape; second order: waviness; third order: roughness-grooves; fourth order: roughness-scoring, flakes, domes).
Tactile measurement instruments are often used to determine characteristic surface values on workpieces. With tactile measurement instruments, a diamond tip is moved over the surface for a determination of the roughness. This instrument has an inductive converter. A sensor with a diamond tip travels over the surface of the workpiece at a right angle to the direction of the groove, and the perpendicular stroke of the stylus tip is converted into an electric signal in the inductive converter. This measurement signal of the primary profile is usually entered into a computer processor with the help of an analog-digital converter.
Such a surface testing instrument operates unidirectionally, i.e., the sensor with the diamond tip can be drawn in only one direction relative to the workpiece surface. This surface testing device has three components: the sensor, the feed mechanism and the evaluation unit with display and documentation.
The sensor converts the vertical movement of the stylus tip into an electric signal. To do so, the sensor has the inductive converter and a stylus tip in a high-precision mount. In addition, the sensor may also have a skid. There are numerous different sensor shapes with a wide variety of geometric shapes to be measured, such as surfaces, waves, boreholes, involutes, etc. Basically, a distinction is made between single-skid sensors, dual-skid sensors and reference plane sensors. Sensors with skids are used mainly in handheld devices. The skid follows the ripple or waviness. It acts as a high-pass filter and does not take into account the macroscopic shape of the profile. Skid sensors do not provide accurate information about shape and waviness. Such sensors are used mainly in workshops. The reference plane sensor system performs measurements against a reference surface and thus supplies an almost undistorted map of the primary profile. Diamond cones with a rounded tip are used as the stylus. Nominal values for the stylus tip include the tip radius (e.g., 2 μm, 5 μm or 10 μm) and the cone angle of the diamond cone, i.e., its tip, at 60° or 90°, for example.
The feed unit guides the sensor over the workpiece surface continuously and at a constant speed. A distinction is made between feed units with or without a reference plane and rotary feed units. Most measurement instruments have a feed unit with a built-in reference plane. These make it possible to use sensors with and without skids. Feed units without a reference plane only allow the use of sensors with skids. Only feed units with a built-in plane of reference in combination with a sensor without a skidless sensor allow accurate determination of the shape, waviness and roughness. The precision of the shape measurement depends primarily on the precision of the reference plane. A rotary feed unit rotates a cylindrical specimen beneath the stationary sensor. Concentricity errors in a workpiece can be eliminated by using sensors with skids.
However, this type of surface testing device is problematical when used in the production of workpieces inasmuch as the workpiece must be unchucked from the spindle on the machine tool and introduced into the surface testing device in order to measure its roughness. This is a disadvantage because rechucking of the workpiece in the machine tool usually results in a loss of dimensional stability in further machining in relation to the machining steps performed previously. The surface properties of a workpiece are therefore usually not tested until after completion of the machining in the machine tool. However, reworking is then possible only in exceptional cases. Thus, for example, failure to conform to the required surface properties will cause rejection of a workpiece.
The machining operation must therefore be stopped, and the working area of the machine tool must be made accessible to a worker in order to test the surface properties of the workpiece during the machining of same in the machine tool. Then, by using a manual surface testing device, the worker can check on whether the workpiece has the required surface properties.
Next, the measurement result must be analyzed and evaluated to ascertain:    a) whether the required surface property has been reached and the workpiece is acceptable;    b) if the required surface property has not been achieved, whether the workpiece can be reworked even if it is not acceptable; or    c) if the required surface property has not been achieved, whether the workpiece is not acceptable and also cannot be reworked.
Now the machining may be continued, if necessary,
However, this is so time-consuming that it cannot be carried out for inspecting the required surface property on each individual workpiece, although it can be used for statistical testing of a manufacturing lot.
Furthermore, within the framework of statistical testing, it is possible to ascertain:    a) whether the workpiece is acceptable;    b) whether the machining parameters (feed, rotational speed, cutting depth, etc.) are acceptable, and    c) whether the machining conditions are acceptable (vibration of the machine tool, spindle rotation, etc.).
Furthermore, many surfaces are not even accessible to portable testing devices.
In addition, because of the given geometric relationships and measurement principles, measurement of the surface property of a borehole in a workpiece using known surface testing devices can be carried out in the longitudinal direction of the borehole but not along the circumference. Thus it is impossible in terms of space, for example, to guide a sensor with a diamond tip along a circumferential line of a borehole with 5 mm to 150 mm, for example, over the surface of the borehole in the workpiece and thereby detect the stroke of the stylus tip in a direction orthonormal to the surface of the borehole. Such measurements have been possible in the past only by using special instruments under laboratory conditions.
Consequently, the evaluation of surface roughness has been possible so far only as a downstream control step or as a manual operation on the workpiece while it is chucked. Despite wear or micro eruptions on the blade, the manufacturing dimension in many machining steps may still be within the tolerance or the intervention limits. However, the surface roughness may already be outside of specification. The missing element for monitoring surface quality near the process is a device for measuring roughness, which is used in a fully automatic operation in the machine tool. Neither the manual internal roughness measurement nor the traditional external roughness measurement provides such a practical approach.
Devices and methods for measuring a contour in a machine tool are known from the prior art. In this context, for example, the document DE 10 2007 041 272 A1 describes a measurement system with a multidimensional measurement sensor arrangement for a contact measurement with stationary and rotating tools in a machine tool. The measurement system is disclosed with different sensor elements having a pyramidal or (truncated) conical shape for performing the contour measurement. However, only the dimensions of a stationary tool are determined with the measurement sensor here. This arrangement is not suitable for performing measurements on a workpiece.
Another multidirectional measurement sensor for carrying out contour measurements is known from DE 102 62 188 B4, which has a holder for replaceable styluses. This document also describes different styluses having spherical or disk-shaped scanning heads. In addition, scanning heads having a plurality of hemispherical and disk-shaped stylus geometries that can be used independently of the direction of contact have been described.
One device for measuring roughness is known from DE 102 06 146 A1. This document discloses a vibration detection system having a stylus construction with a stylus but is embodied as an inclined cylinder having a disk-shaped contact point.
The brochure “Precision tools, Precicom 225” from the company Precitool Werkzeughandel GmbH & Co. KG discloses styluses and stylus systems for measuring contour and roughness. This document discloses two conical stylus tips with a diamond intended for measuring roughness.
Another device and another method for measuring contour and roughness are described in DE 199 47 001 A1. This document describes an instrument for measuring the surface contour and roughness which is suggesting the measuring force at an assumed value when at least the stylus or the stylus holder has been replaced.
Finally, US 2002/0 059 041 A1 discloses a device and a method for measuring contour and roughness in a machine tool. The device can be mounted instead of the tool in a machine tool.
Problem
For measuring the surface property, in particular roughness of subsections of surface on a workpiece, a method and/or a device are to be made available for increasing productivity and for maintaining the highest possible quality demands.
Approach
Therefore, a multidirectional roughness measuring insert for determining a measurement variable that is characteristic of the roughness of a surface is proposed, comprising a carrier body, on which a stylus holder is arranged for holding a stylus, an analog sensor, which converts the movements of the carrier body into measurement signals that are characteristic of the roughness of a surface of a workpiece, a stylus that can be connected to the carrier body and includes a rod-shaped shaft and a scanning head mounted on the shaft, wherein the scanning head is at least one portion of an at least essentially rotationally symmetrical test body in relation to a portion of the rod-shaped shaft, or wherein the scanning head is at least one portion of an essentially rotationally symmetrical test body, which is arranged on a distal end of at least one portion of the rod-shaped shaft. The essentially rotationally symmetrical test body has a double conical shape or a double truncated conical shape. A region of the largest diameter (equator) of the test body is designed as the contact point with a surface of a workpiece to be measured, wherein the contact point is formed by two double conical or truncated double conical lateral surfaces and the contact point is rounded in the region of the largest diameter of the test body,
This arrangement allows the use of a measuring sensor that performs an analog measurement in a spindle in a machine tool instead of using a tool. To do so, a measurement sensor having an analog measurement function is combined with one of the styluses described here to perform roughness measurements. The measuring sensor is a measuring sensor that performs an analog scan and is used as the replacement for the roughness measurement in the spindle of the machine tool, transmitting the measured data or roughness values calculated in a processor in the measurement sensor or the like (via an infrared or wireless interface) or in a hard-wired action to the controller of the machine tool. A measurement sensor that performs an analog scan supplies a measurement signal, which reflects an increase and a decrease in the deflection of the stylus of the measurement insert. This is to be seen in contrast with a digital scanning measurement sensor, which supplies an on-off signal or an off-on signal only when the stylus is deflected out of its resting position by a predetermined amount.
One variant of such a measurement sensor functions with a rotationally symmetrical measuring unit, for example, in which an analog measurement signal is generated from the shadow of a miniature light barrier. The start of the shadow of the light barrier is detected by deflection of the stylus out of its resting position by a predetermined amount. The analog measurement signal may also reflect the rise and fall in the shadow, occurring when the stylus of the measurement insert is deflected to a greater or lesser extent. An analog measurement signal is generated in this way,
The variants of the roughness measurement insert presented here are multidirectional inasmuch as a surface of a workpiece can be scanned from any direction due to the rotationally symmetrical measuring unit in combination with the specific stylus designs.
For example, it is thus possible with the multidirectional roughness measurement inserts to insert the stylus into a borehole or a recess cut into a workpiece and then to scan laterally on the wall of the borehole or the milled recess in any orientation of the roughness measurement insert. This is impossible with traditional roughness measurement devices because when using the diamond cone tip, a measurement can be performed only in the direction of its cone tip.
Using the multidirectional roughness measurement inserts, which are to be inserted into a spindle of a machine tool, the machine tool is used as a feed device. In addition, the machine tool also supplies the required reference plane.
In one variant of the multidirectional roughness measurement insert, it is designed with a housing in which an annular support bearing is formed, defining an X, Y bearing plane and a central axis Z of the roughness measurement insert that is normal to the former. The roughness measurement insert has a carrier body on which a stylus holder is arranged centrally to hold a stylus. The roughness measurement insert additionally has a transmission element, which is displaceably guided along the central axis Z in the housing to convert any deflection of the carrier body out of its resting position and into linear movements. In its resting position, the transmission element is aligned with the central axis Z in at least some sections. The roughness measurement insert also has an analog sensor that converts the linear movements of the transmission element into measurement signals that are characteristic of the roughness of a surface of a workpiece. A stylus-shaped component or the stylus comprising the rod-shaped shaft and the scanning head mounted on the shaft is coupled to the transmission element. The scanning head of the multidirectional roughness measurement insert comprises at least one section of a test body, which is essentially rotationally symmetrical to the central axis Z.
The analog sensor here may be a light barrier of the type described above.
With the multidirectional roughness measurement insert, the rod-shaped shaft may be coupled directly or indirectly to the transmission element in a linear extension or may be bent at an angle of approx. 0° to approx, 40°, coupled directly or indirectly to the transmission element. The rod-shaped shaft may be connected to the transmission element or to the carrier body, bent at an angle of approx, 20° to approx. 30°, preferably approx. 25°. If one surface cannot be reached with such an arrangement, a bit of 90° in the shaft is also possible.
With the multidirectional roughness measurement insert, the contact point may be formed by at least one sections of two double cone or double truncated cone lateral surfaces wherein the contact point is rounded in the region of the largest diameter of the test body.
The contact point may be defined as a function of the expected surface roughness, the path in the direction of advance of the workpiece or of the roughness measurement insert traveled per revolution or per stroke, the forward feed or the tool geometry, the tool geometry [sic] and the tool strength.
The contact point of the test body of the multidirectional roughness measurement insert may have a radius of approx. 0.4 mm to approx. 3 mm, a respective cone angle of approx, 30° to approx. 70° in the range of the largest diameter or circumference or radius. It holds here that at the largest circumference, i.e., at the equator of the test body, it does not have a circular shape but instead may also have an elliptical shape or some other cross-sectional shape that deviates from the circular.
The contact point of the test body of the multidirectional roughness measurement insert may have an edge radius of approx. 5 μm to approx. 50 μm in the region of the largest diameter. The curvature of the contact point of the test body may have a constant value or the curvature may change along a curved region of the contact point of the test body. The latter variant detects embodiments in which the edge does not have an edge rounding to be described with a radius at the largest diameter or at the largest circumference, i.e., at the equator of the test object, but instead has a parabolic edge form or a spline-shaped edge form or some other edge form.
In the multidirectional roughness measurement insert, the contact point of the test body may have a double conical shape or a double truncated conical shape with a radius in the range of the largest diameter from approx. 1.5 mm to approx. 5 mm or from approx. 0.4 mm to approx. 3 mm, an edge radius of approx. 5 μm to approx. 50 μm and a respective cone angle of approx, 30° to approx. 130°. In one variant, the two cone angles may be approx, 90°, the radius in the region of the largest diameter may be approx, 1.5 mm, and the edge radius may be approx. 40 μm. In another variant, the two cone angles may be approx. 120°, the radius in the region of the largest diameter may be approx. 1.1 mm and the edge radius may be approx, 10 μm. In another variant, the two cone angles may be approx. 60°, the radius in the region of the largest diameter may be approx. 1.5 mm and the edge radius may be approx. 20 μm.
The contact point of the test body of the multidirectional roughness measurement insert may have a forward direction oriented at least approximately in the axial direction of the largest radius.
The multidirectional roughness measurement insert may be designed with a processing unit coupled to the analog sensor in order to determine from the measurement signals at least one measurement variable that is characteristic of a surface wherein the processing unit is arranged either in the housing of the roughness measurement insert or is arranged separately thereof.
The measurement of the roughness with this roughness measurement insert depends greatly on the ability of the scanning head to detect unevenness and then to maintain precision at the point of contact. A multidirectional roughness measurement insert of the type described here has a stylus which physically comes in contact with a surface to be measured and has a measured value converter for converting the movement of the stylus into an electric signal, which is then processed further. The part of the stylus that is in contact with the surface is the scanning head. The scanning head is designed with a profile shape adapted to the measurement task integrated into the production sequence of the workpiece. Based on its finite shape, some profiles of the scanning head have a greater effect on or a better interaction with the surface to be measured than others. The size and shape and/or profile of the stylus must be selected carefully. These features have an influence on the information obtained during the roughness measurement. Pins and sensors comprise slender shafts with contact tips or heads for measuring the roughness of surfaces on workpieces in a machine tool during the manufacturing process.
With the variants of the multidirectional measurement sensor disclosed here, the stylus has a cylindrical rod or a slender cone with a scanning head that is rotationally symmetrical with the central longitudinal axis of the stylus. A stylus is a narrow elongated shaft, similar in shape to a ballpoint pen. The stylus may be slightly cambered, so that it can be gripped more easily. For roughness measurements, the scanning heads are usually made of ruby, a hard metal or ceramic materials. Styluses or scanning heads come in contact with the workpiece to perform measurements of roughness. In general, the scanning head consists of a single piece of material, but a few styluses or scanning heads consist of an insert made of ruby or diamond, soldered, pressed or glued into/onto the head. The material of the scanning head may have an influence on the measurement. For example, the scanning head may be an Al2O3 ruby body made of synthetic monocrystalline ruby, a silicon nitride body made of hard pressed Si3N4, a zirconium oxide body made of sintered ZrO2, a hollow body made of white aluminum Al2O3 sintered ceramic, a disk of silver steel, a simple silver steel disk made of silver steel, a silver steel cylinder disk made of silver steel, a cylinder disk made of synthetic ruby ending in a ruby body, a cylinder made of tungsten carbide, ending in a tungsten carbide disk, a silver steel disk made of silver steel with a peripheral edge angle of 30° to 120°, with a rounded peripheral edge made of tungsten carbide or some other material.
The rod or shaft may be made of different materials including nonmagnetic stainless steel, ceramic and carbon fibers. Disk-shaped scanning heads are thin sections of a double cone containing its equator.
A large disk diameter reduces the impact and/or pressure on the workpiece surface whose roughness is to be tested. A relatively slender shaft ensures flexibility in accessing certain measurement sites.
In another variant, the multidirectional roughness measurement insert may also permit, in addition to a roughness measurement, a determination of a measured value that is characteristic of the contour of a surface. Such a variant of the roughness measurement insert makes it possible to carry out both a contour measurement and a roughness measurement using the same tool insert. When using such a variant of the roughness measurement insert, it is not necessary to replace the tool insert to carry out the different measurements, which would claim additional cycle time in the event of a procedural application.
In one such variant, the multidirectional roughness measurement insert may have a stylus with a first scanning head for the roughness measurement and a second scanning head for the contour measurement. The first scanning head, corresponding to the variants of the roughness measurement insert described above, is at least one section of an essentially rotationally symmetrical and essentially disk-shaped first test body. The second scanning head may comprise at least one section of an essentially spherical or ellipsoidal test body. The second scanning head may be arranged on a distal end of at least one section of the shaft of the stylus. In this embodiment, the second test body may be essentially rotationally symmetrical to this section of the shaft. The contact point of the second scanning head may correspond to the lateral surface of the section of the second test body.
In a first variant, the first scanning head and the second scanning head may be arranged on a distal end of at least one section of the shaft of the stylus. The first test body and/or the second test body may be rotationally symmetrical to the section of the shaft. Alternatively, the axes of rotation of the first test body and/or of the second test body may not correspond to the axis of rotation of the section of the shaft. In addition, the stylus may have a test body comprising the first scanning head and the second scanning head, wherein the test body may be arranged on the distal end of one section of the shaft. The first scanning head may be arranged in a first region of the test head, and the second scanning head may be arranged in a second region of the test head, The first region and the second region may be on two opposite and/or adjacent sides of the test head. The test head may be provided in one or more pieces.
In a preferred embodiment, the test head had an essentially spherical or ellipsoidal shape, except for the first region in which the first scanning head is formed and except for a region in which the test head is connected to the section of the shaft. In the region of the second scanning head, the shape of the test body thus corresponds to the shape of the second test body. In this configuration, the test body may have a missing spherical and/or ellipsoidal section in the first region, such that a spherical and/or ellipsoidal surface is formed on the test head, The first scanning head may protrude centrally and/or orthogonally out of the circular or ellipsoidal surface. Alternatively, in the first region, the test head may have a section in the form of a cylindrical body on which the first scanning head is provided. The cylindrical body may be rotationally symmetrical with the first test body, wherein the radius of the cylindrical body is preferably smaller than the radius in the region of the largest diameter of the first test body.
In an alternative variant, the stylus may have the first scanning head arranged on a distal end of the first section of the stylus and may have the second scanning head arranged on a distal end of the second section of the stylus. In a preferred embodiment, the first section having the first scanning head is designed as the axial extension of the shaft of the stylus. The second section having the second scanning head may be arranged proximally in front of the first section on the shaft. In addition, the second section may be orthogonal to the first section. In another conceivable embodiment, the second scanning head is provided on the distal end of the first section, which is formed in the axial extension of the shaft, and the first scanning head is provided on the distal end of the second section arranged orthogonally to the shaft. Alternatively, the first section and the second section may be provided on the distal end of the shaft and orthogonally to it. The first section and the second section may be provided on opposite sides of the shaft. In addition, the longitudinal axes of the first section and of the second section may be orthogonal or parallel to one another. An embodiment in which the longitudinal axes of the first section and of the second section are equivalent is also conceivable.
The multidirectional roughness measurement insert can be moved by a machine tool into a measurement space relative to the surface of the workpiece to be measured. The roughness measurement insert, which functions through contact, detects the surface of the workpiece on contacting same. For each deviation in shape of the real workpiece surface from its ideal shape, the multidimensional roughness measurement insert delivers corresponding measurement data to its processing unit. The processing unit may contain a computer program. The waviness profile and the roughness profile can be determined there by digital filtering, and characteristic variables can be calculated, such as the arithmetic mean roughness, the square mean roughness, the depth of roughness, the maximum individual depth of roughness, the mean smoothing depth, the mean groove depth, the mean groove width, the corrugation depth, the profile depth, etc.
A stylus of the type presented here for use in a multidirectional roughness measuring instrument has a rod-shaped shaft and a scanning head mounted on the shaft, wherein the scanning head is at least one section of a test body that is at least essentially rotationally symmetrical to at least one section of the rod-shaped shaft, or the scanning head is at least one section of an essentially rotationally symmetrical test body arranged on a distal end of at least one section of the rod-shaped shaft. The essentially rotationally symmetrical test body has a double conical shape or a double truncated conical shape, A region of the largest diameter (equator) of the test body is designed as a contact point to a surface of a workpiece to be measured, wherein the contact point is formed by two double conical or double truncated conical lateral surfaces, and the contact point is rounded in the region of the largest diameter of the test body.
This can be seen in differentiation from the traditional roughness measurement devices, which use a diamond tip, for example, which is mounted laterally on a rod in the manner of a phonograph record player needle.
Measurements with these scanning heads, which do not conform to a standard, may lead to measured values which do not conform to a standard in the ongoing production process but instead the approximation values. However, these approximation values can easily be compared with quality assurance measurements by means of comparative measurements.
A roughness measuring method presented here for determining a measurement variable that is characteristic of the roughness of the surface of a workpiece uses a roughness measurement insert of the type described above. The following steps are carried out in this method:    Bringing the scanning head in contact with the surface to be measured, so that the scanning head assumes a predefined deflection out of its resting position;    Adjusting the test load by additional approach or retraction of the roughness measurement insert in relation to the surface to be measured, wherein the adjustment of the test load (pressing force of the scanning head based on the contact surface of the scanning head on the surface to be measured) as a function of the shape of the scanning head and the shape of the surface of the workpiece to be measured;    Activating a “roughness measurement” mode, in which measurement signals detected as described below are recorded and/or processed;    Traveling a predetermined measurement distance along a predetermined measurement direction;    Converting the movements of the stylus into measurement signals that are characteristic of the roughness of the surface and optionally recording them and/or processing the measurement signals;    Evaluating the measurement signals to determine at least one measurement variable that is characteristic of the roughness of a surface; and    Sending at least one measurement variable thereby determined to a machine control unit.
With this roughness measurement method, the step of bringing the scanning head into contact with the surface to be measured can be carried out by the approach of the roughness measurement insert in a machine tool relative to the surface of the workpiece to be measured.
The step of traveling a predetermined measurement distance along a predetermined measurement direction may comprise either specifying a path distance to be traveled by the scanning head or specifying a period of time during which the scanning head will travel the measurement distance, and the predetermined measurement direction may comprise any direction to be selected along the surface to be measured.
The step of evaluation of the measurement signals—in a processor in the roughness measurement insert or downstream—may comprise saving and linking the measurement signals recorded by means of the analog sensor to form at least one of the measured values that are characteristic of the roughness of the surface: arithmetic mean roughness, average peak-to-valley height, square mean roughness, maximum individual depth of roughness, depth of roughness, mean smoothing depth, mean groove depth, mean width of scoring, corrugation depth, profile depth. In addition, information about design deviations of the first and second order may also be supplied.
The step of evaluation of the measurement signals recorded by means of the analog sensor also comprises a processing of the measurement signals by means of a profile filter because otherwise the waviness will falsify the roughness value. A profile filter, for example, a digital phase-corrected Gaussian filter, separates the unfiltered primary profile (P profile) into roughness (R profile) and waviness (W profile). The roughness profile is the primary profile deviation from waviness (R=P−W). The reference line and/or the center line in the roughness profile is/are the line corresponding to the long-wave profile fractions, which are determined by the Gaussian filter and are suppressed. When using the Gaussian filter, the distortions in the profile in the vertical direction are reduced due to the sudden change in height of the profile. The phase shift in the horizontal direction is completely omitted. To determine the center line, the weighted arithmetic mean of the ordinate heights is calculated at each point with the help of the Gaussian filter. In order for points at the beginning and end of the measurement zone to also be weighted correctly, the scanning distance must be longer than the total distance for fade-in and fade-out of the filter. The forward distance and the trailing distance of half the cut-off wavelength each are customary at any rate.
The cut-off wavelength of a profile filter is the wavelength at which the filter reduces the amplitude of a sinus wave by one-half. It may thus be understood to be a measure for the boundary between roughness and waviness. The cut-off wavelength defines the transition from roughness to even shorter wavelengths and the cut-off wavelength delimits the waviness with respect to longer wavelengths. The cut-off wavelengths in the case of periodic profiles are to be selected according to the average groove width and in the case of aperiodic profiles according to roughness value to be measured. The total measuring distance of a measurements is always five times the cut-off wavelength. The scanning distance is six times the cut-off wave-length. The amplitude of the filtered roughness profile decreases at a lower cut-off wavelength, and the amplitude of the waviness profile increases at a lower cut-off wavelength. Smaller roughness values are therefore also measured at shorter cut-off wavelengths.
Roughness parameters are calculated from the filtered profile. The cut-off wave-length used is therefore relevant in comparative measurements in particular. The primary profile, the waviness and roughness are differentiated. The value of a profile characteristic variable is obtained by averaging the individual results of individual measurement distances directly one after the other.
The arithmetic mean roughness is the arithmetic mean of the amounts of the ordinate values of the roughness profile inside the individual measurement distance. It represents the mean deviation of the profile from the center line.
The mean roughness value cannot differentiate between peaks and valleys, nor can it recognize different profile shapes. Its definition is based on a strong averaging.
The square mean roughness value is the square mean value of the profile deviation. It is defined like the mean roughness value but it has a more sensitive response to individual peaks and grooves.
The average peak-to-valley height is the sum of the height of the largest profile peak and the depth of the largest profile valley within a single measurement distance. The average peak-to-valley height is usually obtained by averaging the results of five individual measurement distances. On the whole, the average peak-to-valley height shows a more sensitive response to a change in surface structure than does the mean roughness value.
The maximum individual peak-to-valley height is the largest individual peak-to-valley height.
The peak-to-valley height is the vertical difference between the deepest valley and the highest peak within the total measurement distance.
The following roughness parameters are of assistance in “horizontal” characterization of a profile.
The definition of the average smoothing depth is almost identical to that of the average peak-to-valley height. The filtered profile is divided into five equal distances corresponding to the cut-off wavelength. In contrast with the determination of the average peak-to-valley height, the distance from the center line to the highest peak is determined in each segment here. The average smoothing depth is the arithmetic mean of these five values.
The average peak-to-valley height is formed like the average smoothing depth. The reference depths are used instead of the peak heights.
In the case of bearing surfaces, grooves serve as pockets of lubricant, for example. Peaks in turn are not desirable because they increase both friction and wear. In the case of interference fits, it is often common to work with the average smoothing depth because interference fits require the largest possible contact area.
The average groove width is the arithmetic mean of the widths of the profile elements of the roughness profile within a single measurement distance. A profile element here is a profile elevation with a neighboring recess. The average groove width is obtained by averaging the results of five individual measurement distances. It is used in periodic profiles for selecting the cut-off wavelength of the filter.
The corrugation depth indicates the maximum depth of the filtered profile after the roughness has been filtered out.
The profile depth is the distance between two parallel lines enclosing the unfiltered surface profile. The lines are in the form of the ideal profile (e.g., straight line, circle).
The roughness measurement method described here is characterized in that the above method steps are carried out on a machine tool, wherein the roughness measurement insert is used instead of a tool in a spindle on the machine tool and the measurement signals and/or the measured variable is/are output to a machine controller of the machine tool.
The method steps can be performed before and/or after processing steps by means of at least one tool on the workpiece in the machine tool.
The multidirectional roughness measurement insert may be oriented along a predetermined measurement direction in the step of traveling along a predetermined measurement distance, so that the contact point of the test body has a feed direction, which is oriented at least approximately in the axial direction of the larger radius of the test body, and the tangential direction of the larger radius is aligned at least approximately in parallel with a groove direction to be measured on the workpiece.
The roughness measurement inserts presented here offer the following advantages:    (a) Minimizing rejects due to direct monitoring of the manufacturing process    (b) Rotary and milling tools can be operated up to their wear limit without any negative effect on the peak-to-valley height    (c) Higher productivity and process reliability due to the omission of manual and downstream tests.
The roughness measurement inserts presented here for measuring workpiece surfaces can be integrated directly into the machining operation. Due to the process-integrated monitoring of the workpiece surfaces, the manufacturing processes are much more efficient than previously.
A possible reduction in the downtime of the machine tool is achieved by eliminating tedious manual roughness measurements. The cost for rejects due to immediate reworking are minimized. Tools can be operated up to their wear limit and need not be replaced as a precautionary measure.